The kinesin motor protein family generates force and movement along microtubules by an as-yet unknown chemical mechanism. Key roles are served in kinesin's force-generation cycle by the power-giving ATP substrate and the tubulin against which motion is generated. We are conducting experiments to characterize the interactions between kinesin, nucleotide, and tubulin. The effect of chemical transitions in the bound nucleotide on the atomic structure of kinesin is being examined by X-ray crystallography studies of complexes between kinesin and chemical variants of ATP. No form of tubulin is known to be compatible with X-ray crystallography studies, but structural data indicate that a short C-terminal segment of b-tubulin contributes most of tubulin's so-called 'major' interaction with kinesin. Variants of this C-terminal peptide will be constructed and assayed for kinesin-binding activity, ability to catalyze kinesin ATPase, or ability to competitively inhibit the microtubule-stimulated ATPase reaction. Peptides with kinesin interactions that are functionally similar to those of tubulin will be co-crystallized with kinesin, in each of the high-tubulin-affinity nucleotide forms of kinesin, and these complexes characterized by X-ray crystallography. These experiments provide the first direct structural information describing the kinesin-microtubule binding interaction, and could provide a structural explanation for the kinesin-bound nucleotide's ability to modulate this interaction. Computer graphics resources are essential to this project because our ultimate goal is to generate a three-dimensional atomic-resolution model of the motor mechanism of kinesin. Our structural determination and refinement efforts require significant amounts of interactive graphics computing.